X-Ray Substructure Studies of Four Galaxy Clusters Using XMM-Newton Data

Mahdavi et al. find that the degree of agreement between weak lensing and X-ray mass measurements is a function of cluster radius. Numerical simulations also point out that X-ray mass proxies do not work equally well at all radii. The origin of the effect is thought to be associated with cluster mergers. Recent work presenting the cluster maps showed an ability of X-ray maps to reveal and study cluster mergers in detail. Here, we present a first attempt to use the study of substructure in assessing the systematics of the hydrostatic mass measurements using two-dimensional (2D) X-ray diagnostics. The temperature map is uniquely able to identify the substructure in an almost relaxed cluster which would be unnoticed in the intracluster medium electron number density and pressure maps. We describe the radial fluctuations in the 2D maps by a cumulative/differential scatter profile relative to the mean profile within/at a given radius. The amplitude indicates ~10% fluctuations in the temperature, electron number density, and entropy maps, and ~15% fluctuations in the pressure map. The amplitude of and the discontinuity in the scatter complement 2D substructure diagnostics, e.g., indicating the most disturbed radial range. There is a tantalizing link between the substructure identified using the scatter of the entropy and pressure fluctuations and the hydrostatic mass bias relative to the expected mass based on the M-Y _X and M-M _gas relations particularly at r ₅₀₀. XMM-Newton observations with ~120,000 source photons from the cluster are sufficient to apply our substructure diagnostics via the spectrally measured 2D temperature, electron number density, entropy, and pressure maps.

This work is based on observations made with the XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).